To combine like terms, add or subtract the coefficients (the numbers that come before the variables) of terms that have the same variable raised to the same exponent.

4a⁶ - 4a⁶ = 0a⁶

You can only add or subtract monomials that have the same variable and the same exponent. For example, 2a + 4a = 6a and 4a² - a² = 3a² but 2a + 4b and 7a - 3b cannot be combined. However, you can multiply and divide monomials with unlike terms. For example, 2a x 6b = 12ab.

Perimeter is equal to the sum of the four sides:

p = a + b + c + d
p = 6 + 5 + 2 + 5
p = 18

The first step to solve a quadratic expression that's not set to zero is to solve the equation so that it is set to zero:

x² - 17x + 25 = -5x - 2
x² - 17x + 25 + 2 = -5x
x² - 17x + 5x + 27 = 0
x² - 12x + 27 = 0

Next, factor the quadratic equation:

x² - 12x + 27 = 0
(x - 3)(x - 9) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (x - 3) or (x - 9) must equal zero:

If (x - 3) = 0, x must equal 3
If (x - 9) = 0, x must equal 9

So the solution is that x = 3 or 9

Parallel lines are lines that share the same slope (steepness) and therefore never intersect. A transversal occurs when a set of parallel lines are crossed by another line. All of the angles formed by a transversal are called interior angles and angles in the same position on different parallel lines equal each other (a° = w°, b° = x°, c° = z°, d° = y°) and are called corresponding angles. Alternate interior angles are equal (a° = z°, b° = y°, c° = w°, d° = x°) and all acute angles (a° = c° = w° = z°) and all obtuse angles (b° = d° = x° = y°) equal each other. Same-side interior angles are supplementary and add up to 180° (e.g. a° + d° = 180°, d° + c° = 180°).